Macrophages have been implicated in the pathogenesis of several autoimmune diseases, such as systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), multiple sclerosis, and inflammatory bowel disease. Recent exciting advances in the genetics of human autoimmune diseases have linked allelic variants of genes important in macrophage activation with human autoimmune diseases. Examples include linkage of ITGAM that encodes the 1M component of the 1M22 integrin, FCGR2A (Fc3RIIA), and TNFAIP3 (A20) with SLE and/or RA. 1M22 and Fc3Rs are receptors for factors strongly implicated in autoimmune pathogenesis, namely complement degradation products and immune complexes, and A20 regulates signaling by pathogenic TNF and Toll-like receptors. The long term goals of this project are to understand signaling crosstalk mechanisms that regulate macrophage activation and cytokine production in the context of human autoimmune diseases. We have focused on mechanisms of cytokine signaling and production that are regulated by ITAM-associated receptors important in disease pathogenesis, such as 1M22 and Fc3Rs. Signaling by immunoreceptor tyrosine-based activation motifs (ITAMs) regulates macrophage responses to key inflammatory factors including TNF, interferons and Toll-like receptors (TLRs). ITAM- associated receptors can have either activating or inhibitory effects, depending on cell context. ITAM- mediated activating mechanisms are well characterized. In contrast, ITAM-mediated inhibitory mechanisms have been more recently described and are not well understood, even though they are highly relevant for downregulation of inflammation. In this project we have identified a new and potent ITAM-mediated inhibitory pathway induced by 1M22 and Fc3Rs that deactivates macrophages. This pathway cross-inhibits responses to TLRs and type I IFNs that have been implicated in RA and SLE pathogenesis. Inhibition is dependent on the ITAM-containing adaptor DAP12 and works indirectly through activation of STAT3 and the induction of signaling inhibitors including SOCS3 and A20. Induction of this pathway was dysregulated in RA synovial macrophages. We hypothesize that this inhibitory pathway is important for limiting macrophage activation and cytokine production, and its effectiveness in limiting inflammation in human autoimmune diseases is modulated by disease-associated polymorphisms and environmental factors. In this application, we will investigate molecular mechanisms and pathways by which ITAM- associated receptors inhibit macrophage function and regulate cytokine production. We will use predominantly human systems and cells that are directly relevant for autoimmune disease pathogenesis, and study the function of autoimmune disease-associated gene products 1M22, Fc3Rs and A20. We anticipate that our studies will yield insights into regulation of cytokine production that can be exploited for therapeutic interventions to suppress autoimmunity and inflammation.